The present invention relates, in general, to pipe organs, electronic organs, and associated musical instruments. In particular, it relates to that portion of these instruments commonly called "stops" or "stop controls", which are used by the organist or player to select the desired musical tone colors. These controls are mechanical switches which are sometimes referred to as drawknobs, tilting tablets, or the like.
In the course of playing music on instruments such as pipe or electronic organs, the player operates the various stops or stop controls in various combinations and at selected times to produce the variety of musical tones which such instruments are capable of providing. It is sometimes necessary or desirable for the player to operate numerous individual stop controls at one time, and for this reason it is common practice in the design and construction of organs to provide the player with at least one separate control, and usually several controls, which will permit the player to change the position of several stop controls all at the same time by pressing a single button, which is commonly called a "combination piston". Most organs have numerous combination pistons which provide the player with the ability to operate selected groups of stop controls at will by having each selected group or combination of stops assigned to a single corresponding combination piston. Such an arrangement requires that each stop control must be able to be operated either manually to permit individual stop controls to be actuated by the player, or electro-mechanically, so that the individual stop controls can be operated in combinations as a result of the player activating a combination piston.
To those familiar with the art, it is well known that noise is a problem when electro-mechanical switches are operated, and such noise is especially undesirable in musical instruments such as organs. Ordinarily, the source of such noise is the various linkages that are required to convert the motion of the drawknobs, tilting tablets, and the like devices to produce switch operation, and the noise is principally the result of the movement of such linkages by means of an electric solenoid, which tends to move the linkages suddenly and rapidly, and such noise is accentuated by the mass of the moving parts.
Another problem in the design of electrically operated stop controls has been the provision of a movement that will provide the organist with a switch that will have a positive "feel" in the movement from an on position to an off position, or vice versa. Such a feel is ordinarily described as a "toggle feel" and enables the player to know that the switch has moved in a positive manner from one position to another. Providing a toggle feel to the drawknob of a stop control has, in the past, required that the moving part of the switch have substantial mass so as to provide inertia for the manual operation. However, this same mass produces problems in the electrically operated mode, since it requires that substantial power be applied through the electric solenoid in order to move the massive switch components.
A typical organ console utilizes a large number of stop controls, so if each control requires a large amount of power for operation, then massive power supplies become necessary, together with heavy cables for carrying the current required to operate large numbers of stop controls simultaneously. This creates an inefficient system, and increases the potential for noise. The efficiency of such systems is further reduced by the friction which is a result of the rubbing together of the various parts of the switch, particularly the movement of an armature core through a solenoid coil in a typical solenoid configuration. Such solenoids are often further affected by corrosion or the accumulation of dirt or dust within the solenoid so that the motion of the switch is often delayed or prevented altogether unless great care is taken to provide frequent, regular maintenance.
Attempts have been made to produce stop controls having lower power requirements by making them of lighter-weight materials. This has resulted in flimsy assemblies having excessive side play or in which the drawknob can rotate.
In addition to the foregoing problems are the difficulties associated with the installation of electro-mechanically operated stop controls in the limited space provided on the drawknob panel, or stop jamb, of an organ. Such jambs may be limited in size in smaller organs, or may be crowded with a multitude of stop controls in larger instruments. Thus, the space limitations inherent in organ consoles have made it difficult to install or service electro-mechanically operated stop controls.
It has been proposed to overcome the foregoing difficulties through the use of magnetic toggle arrangements, wherein a pair of permanent magnets are provided, one mounted on a movable drawknob and the other mounted on a stationary frame adjacent the path of the drawknob so as to repel the first magnet. The repulsion of like poles of the magnets provides a toggle feel to the movement of the drawknob, while allowing the device to be made small enough to fit into an organ console. It has also been provided to operate such devices by means of solenoids driven by electrical pulses produced by small pulse sources in order to avoid the need for large power supplies and connector cables.
However, it has been found that when such permanent magnet devices are driven by pulsed power supplies, problems arise, for the permanent magnets tend to magnetize the pole pieces and movable armatures in the device. When this occurs, the applied pulses must first overcome this magnetization before the desired toggle operation can occur, thereby making the operation of the device nonlinear. Such nonlinearity adversely affects the tolerances of the device, requiring larger pulses than would otherwise be required, and placing restrictions on the location of the permanent magnets, the location of motion-limiting blocks, and the like. This makes it difficult to manufacture such control stops reliably, and counters many of the efficiencies that would otherwise have been provided by the magnetic-repulsion concept.